Method and apparatus for stabilizing

ABSTRACT

A method of and apparatus for stabilizing a vehicular wheel and tire assembly rotatable about an axis and having a circumferential tread which rolls along a surface wherein the method comprises the steps of rotating the wheel and tire assembly while simultaneously determining the radial deviations of the tread with respect to the axis at two or more points along a line across the tread parallel to the axis and rotating about the circumference of the wheel and tire assembly; correlating the determinations thus taken to indicate the curvature of the tread across its width and the irregularity of the tread produced by lateral runout, radial runout or a combination thereof; and subsequently cutting away portions of the tread to redefine the tread so that the irregularity of the tread is substantially eliminated and the curvature of the tread across its width remains the same. The apparatus includes an indicator mechanism, a cutter assembly and a control unit which mounts the indicator mechanism and cutter assembly adjacent the wheel and tire assembly. The indicator mechanism includes one indicator for measuring the radial runout along one edge of the tread, another indicator for measuring the radial runout along the opposite edge of the tread; and means for correlating the indicators to indicate the deviation of the radii across the tread. Another indicator may be provided for correlation with one of the above indicators to indicate the curvature of the tread across its width. The cutter assembly includes a cutter and the control unit includes guide means for controlling the cutter assembly.

United States Patent 1191 Branham et al.

1451 Aug. 14, 1973 METHOD AND APPARATUS FOR STABILIZING [76] Inventors:Norvel R. Branham, 2312 Armand Rd., N.E.; Peter C. Pantaze, 2378 JohnsonRd., N.E., both of Atlanta, Ga.

[22] Filed: Apr. 5, 1971 [21] Appl. No.: 131,506

Related [1.8. Application Data [63] Continuation of Ser. No. 803,030,Feb. 27, 1969,

abandoned.

52 US. Cl. 157/13 51 1m. (:1. B29h 21/01 [58] Field of Search 157/13[56] References Cited UNlTED STATES PATENTS 2,918,116 12/1959 Mooney157/13 3,354,929 11/1967 French 157/13 Primary Examiner-Granville Y.Custer, Jr. Att0rneyNewt0n, Hopkins & Ormsby [57] ABSTRACT A method ofand apparatus for stabilizing a vehicular wheel and tire assemblyrotatable about an axis and having a circumferential tread which rollsalong a surface wherein the method comprises the steps of rotating thewheel and tire assembly while simultaneously determining the radialdeviations of the tread with respect to the axis at two or more pointsalong a line across the tread parallel to the axis and rotating aboutthe circumference of the wheel and tire assembly; correlating thedeterminations thus taken to indicate the curvature of the tread acrossits width and the irregularity of the tread produced by lateral runout,radial runout or a combination thereof; and subsequently cutting awayportions of the tread to redefine the tread so that the irregularity ofthe tread is substantially eliminated and the curvature of the treadacross its width remains the same.

The apparatus includes an indicator mechanism, a cutter assembly and acontrol unit which mounts the indicator mechanism and cutter assemblyadjacent the wheel and tire assembly. The indicator mechanism includesone indicator for measuring the radial runout along one edge of thetread, another indicator for measuring the radial runout along theopposite edge of the tread; and means for correlating the indicators toindicate the deviation of the radii across the tread. Another indicatormay be provided for correlation with one of the above indicators toindicate the curvature of the tread across its width. The cutterassembly includes a cutter and the control unit includes guide means forcontrolling the cutter assembly.

12 Claims, 19 Drawing Figures Patented Aug. 14, 1973 '7 Sheets-Sheet l)I ETEK C. FAA/77425 wbn Patented Aug. 14, 1973 3,752,207

7 Sheets-Sheet 3 //V V /V NORVEL R. BRAIVIMM PETE/2 c. PANTAZE #700600,(76 654 2 ml, M

Patented Aug. 14, 1973 3,752,207

7 Sheets-Sheet 3 .lnnnrnnnnnpnnE-E -I By J FAA/742E.

Vfiuml, M

7 Sheets-Sheet 4 ROTA T/ONAL AX IS /N 1 5 N TORS i 4 5 fiffffifj By Wm,mm,

2 fund, MW

Patented Aug. 14, 1973 7 Sheets-Sheet 5 Patented Aug. 14, 1973 3,752,207

'7 Sheets-Sheet G //V V E /V 70/{5 NORVE L R. BRANHAM PE TER C. PAN TAZEPatented Aug. 14, 1973 3,752,207

7 Sheets-Sheet 7 INVENTORS.

NORVEL R. BRANHAM PETER C. PANTAZE Wm, fi/ilim,

if Wm! M BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates generally to a method of an apparatus for stabilizinga vehicular wheel and tire assembly rotatable about an axis and having acircumferential tread which rolls along a surface and more particularlyto a method of and apparatus for stabilizing a vehicular wheel and tireassembly by substantially eliminating the effects of both radial runoutand lateral runout.

2. Discussion of the Prior Art Commercially available vehicular wheeland tire assemblies normally have what is known in the trade as radialand lateral runout. Radial runout is defined generally as the radialdeviations between the tread of the tire and the axis about which itrotates, and lateral runout is defined generally by the amount ofdisplacement of the tread from a plane perpendicular to the effectiveaxis about which the tread rotates.

Normal production methods employed in the manufacture of automobile andtruck wheels involve the fabrication of a rim and disc secured togetherand manufactured from flat sheet steel. Rims are normally rolled whilethe disc is formed by a stamping operation and the holes are punchedtherethrough through a punching process. In all of 'these manufacturingsteps, the inherent resiliency characteristics of the sheet steelnormally produce both radial and lateral runout in the thusly formedcomponents of the wheel.

To further accentuate the problem, the rim and disc are welded orriveted together to form the wheel. This can sum the already inherentlateral and radial runout as well as adding more radial and lateralrunout to the wheel through distortion.

Lateral and radial runout will also normally be produced in the presentproduction methods for tires because the positioning of the fabricutilized in the manufacture of the tires cannot be uniformly and totallycontrolled on the drum or in the placement of the tire in the matrix,and the normal expansion and contraction of the rubber during its curingprocess cannot be uniformly and totally controlled. Therefore, thepresently used wheels and tires normally have both lateral and radialrunout formed therein.

Since no particular attention is given to radial and lateral runout whenthe tire and the wheel are assembled, the assembly can have a radial andlateral runout of the sum of that produced by the manufacture of thewheel and that produced by the manufacture of the tire. Therefore, it isnecessary to determine and eliminate the effects of both radial andlateral runout of the completed wheel and tire assembly for the desiredoperational performance thereof.

For special applications such as racing vehicles, the wheels formed havebeen machined in an attempt to eliminate the radial and lateral runoutthereof or the wheel is prepared by machining a casting. This attemptwas not only prohibitive costwise, but also failed to eliminate theradial and lateral runout of the tire.

SUMMARY OF THE INVENTION These and other problems associated with priorart apparatus for stabilizing vehicular wheel and tire assemblies areovercome by the invention disclosed herein in that the radial runout andthe results of lateral runout are measured and then the effects thereofsubstantially eliminated to stabilize the wheel and tire assembly as itrotates. The lateral runout itself is not eliminated, but the effecttherof is eliminated by forming a tread which is substantiallyconcentric about the rotational axis of the tire and wheel assembly. Theapparatus for measuring the effect of the radial and lateral runout ofthe wheel and tire assembly also properly orients the cutting assemblyfor proper truing of the tire as well as indicating the amount of treadredefinition that must be performed to properly stabilize the tire andwheel assembly.

The method of the invention includes the step of rotating the wheel andtire assembly about its rotational axis while simultaneously determiningthe radial deviations of the tread with respect to this axis at two ormore spaced points along an imaginary line extending across the treadparallel to the rotational axis and rotating about the circumference ofthe wheel and tire assembly; correlating the measurements thus taken toindicate the difference between the radial deviation determinations madeas the imaginary line is rotated about the tread of the wheel and tireassembly; and subsequently cutting away selected portions of the treadto redefine the tread so that the effect of the lateral and radialrunout is eliminated.

The apparatus of the invention includes generally an indicatingmechanism, a cutting assembly, and a control unit which carries theindicator mechanism and the cutter assembly adjacent the wheel and tireassembly to be stabilized. The indicator mechanism includes a firstindicator for measuring the radial runout along one edge of the tread ofthe wheel and tire assembly; another indicator for measuring the radialrunout along the opposite edge of the tread; and means for correlatingthe indicators to indicate the difference in radial runout between theedges of the tread. The cutter assembly includes a cutter whichredefines the tread in accordance with the indicator readings. Thecontrol unit includes a guide barselectively adjustable to correspond tothe curvature of the tread across its width for controlling the cutterassembly and is movable with respect the indicator mechanism to properlycenter the cutter assembly with respect to the tread of the wheel andtire assembly for the cutting operation.

These and other features and advantages of the invention will becomemore apparent upon consideration of the following specification andaccompanying drawings wherein like-characters of references designatecorresponding parts throughout, and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective viewof theinvention positioned on a tire truing machine;

FIG. 2 is a side elevational view of the indicator mechanism and cutterassembly showing the relative relationship between the same; I

FIG. 3 is a cross-sectional view taken along the center of the controlunit;

FIG. 4 is a top plan view of the indicator mechanism;

FIG. 5 is a front elevational view of the indicator mechanism with thecover removed;

FIG. 6 is a cross-sectional view taken along the line 6-6 ofFIGS. 4 and5;

FIG. 7 is a cross-sectional view taken 7-7 in FIGS. 4 and 5;

along the line FIG. 8 is a cross-sectional view taken along the line 8-8in FIG.

FIG. 9 is a cross-sectional view taken along the line 9-9 in FIG. 5;

FIG. 10 is a cross-sectional view showing the mechanism for adjustingthe angularly positioned guide bar for controlling the cutter mechanismin response to that indicated by the indicator mechanism;

FIG. 11 is an enlarged top plan view of the cover plate showing thewindows therein;

FIG. 12 is an enlarged top plan view of the indicators with the coverremoved showing the indicia thereon;

FIG. 13 is a schematic wiring diagram for the indicator mechanism shownin FIG. 14;

FIG. 14 is a perspective view of an alternate embodiment of theindicator mechanism;

FIG. 15 is a schematic drawing showing radial run out;

FIG. 16 is a schematic drawing showing lateral runout;

FIG. 17 is a perspective view of another alternate embodiment of theindicator mechanism;

FIG. 18 is a top plan view of the indicator mechanism shown in FIG. 17;and

FIG. 19 is a cross-sectional view taken along the line 19-19 in FIG. 18.

These figures and the following detailed description disclose a specificembodiment of the invention; however, the inventive concept is notlimited thereto since it may be embodied in other forms.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS Referring to the figures, itwill be seen that the invention comprises generally an indicatormechanism M, a cutter assembly A, and a control unit U. The control unitU carries both the indicator mechanism M and the cutter assembly A andpositions the same so that the indicator mechanism M can be utilized tomeasure the radial runout and the effect of lateral runout in a tire andwheel assembly and then the cutter assembly A moved into position toproperly true the tire tread 13 for stabilizing the tire and wheelassembly TW, as it rolls along a surface.

Reference to FIG. 15 will indicate that radial runout is the deviation din the radius R as the same is rotated about the tire and wheel assemblyTW, and reference to FIG. 16 will show that the lateral runout is thedisplacement of the tread 13 from a plane perpendicular to itsrotational axis. This forms the subtended angle;

The effect of lateral runout, however, can be determined by measuringthe absolute difference d' between the radii to the tread 13 along animaginary line extending transversely of the tread 13. It will be notedthat at least two comparative measurements must be taken across thewidth of the tread in order that the effect of the lateral runout bedetected.

The effect of lateral runout can be seen ifa cylinder is notperpendicular to its rotational axis but is tilted slightly thereto asseen in FIG. 16. This causes one edge of the circumference of thecylinder to have a long radial dimension at b and a short radialdimension at c while the opposite edge of the circumference of thecylinder has a short radial dimension at w and a long radial dimensionat z located diametrically opposite the corresponding points on the oneedge. There, it will be seen that the axle (not shown) raised off therolling surface rigidly attached to the tire and wheel assembly TW willbe lifted at least twice each time the assembly TW rotates to cause acorresponding vibration to be set up in the axle.

The invention disclosed herein does not remove the lateral runout, butrather eliminates the effect thereof. The tread 13 is redefined to forma concentric surface rotatable about the rotational axis of the tire andwheel assembly TW. This serves to stabilize the assembly TW, itsassociated axle, and hence the vehicle.

Referring to FIG. 1 it will be seen that the invention is mounted on atire truing machine T wherein the tire and wheel assembly TW is mountedon a spindle S and driven by a driving roll D. The invention may be madeas a separate unit for stabilizing a wheel and tire assembly while stillmounted on the vehicle.

The control unit U is mounted on the truing machine T and includes afirst adjustment means 10 for controlling the indicator mechanism M andcutter assembly A along the line of motion B perpendicular to the tiretread 13. Also included is a second adjustment means 11 which controllsthe position of the indicator mecha nism M and the cutter assembly Aalong a line of motion C substantially parallel to the tire tread 13 ofthe tire and wheel assembly TW. The first adjustment means 10 includes abed 12 along which the second adjustment means 11 is slidably carriedand a conventional adjusting screw and hand wheel assembly 14 which isthreadedly connected to the second adjustment means 11 in conventionalmanner to selectively move the second adjustment means 11 therealong asthe hand wheel and screw assembly 14 is rotated.

The second adjustment means 11 is mounted on the bed 12 of the firstadjustment means 10 through a saddle 15 and extends from the firstadjustment means 10 substantially parallel to the tread 13 of the tireand wheel assembly TW. The second adjustment means 1 1 includes a bed 16which mounts a carriage 18 thereon for slidable movement along the lineof motion C. The carriage 18 mounts the indicator mechanism M and thecutter assembly A. A conventional adjusting screw with handwheel. 19extends along the length of the second adjustment means 11 and isthreadedly connected to the carriage 18 to selectively move the carriage18 back and forth along the carriage bed 16 in conventional manner.

A guide bar 20 is mounted on the bed 16 in spaced mounting brackets 21.The guide bar 20 is cylindrical in cross-section and has a semi-circularoffset central portion 22 which controls the position of the carriage 18transversely of the bed 16. One of the mounting brackets 21 is providedwith a locking screw 24 which fixes the rotational and longitudinalposition of the guide bar 20. The brackets 21 permit movement of the bar20 longitudinally with respect to the bed 16 so that the semi-circularporition 22 of guide bar 20 can be centered by use of the handle X withrespect to the tire and wheel assembly TW. The guide bar 20 is markedbyan annular line AL at its center to assist in centering thesemicircular portion 22 of the bar 20 as will be explained hereinafter.

The carriage 18 is provided with a slide plate 26 which slideslongitudinally along the carriage bed 16 but does not move transverselythereof. A saddle 25 fits over the slide plate 26 so that the upperportion of the carriage 18 is selectively extendable transversely of thecarriage bed 16. Referring to FIG. 2, the saddle 25 of the carriage 18is provided with an upstanding pivot bracket 28. Pivotally mountedbetween the bracket 28 and the saddle 25 is a guide follower assembly29.

The guide follower assembly 29 as seen in FIG. 3 receives the guide bar20 therethrough and serves to move the saddle transversely of the bed 16in response to the semi-circular portion 22 of the guide bar 20. Theassembly 29 includes an upper horizontally oriented arm 30 rotatablycarried by the pivot bracket 28 and spaced above the saddle 25. A lowerhorizontally oriented arm 31 is positioned under the upper arm 30 invertical alignment therewith and is rotatably carried by the saddle 25.A vertical connecting plate 33 extends between and is integral with theforward ends of the arms 30 and 31 to maintain their alignment andvertical spacing.

A front guide roll 34 is carried between the upper and lower arms 30 and31 adjacent the plate 33. The guide roll 34 is freely rotatable about avertical axis and engages the guide bar 20.

An adjustable guide unit 35 is carried between the rear ends of the arms30 and 31. The guide unit 35 includes a vertically oriented guide roll36 parallel to the roll 34 and is rotatably mounted on an axle 37. Theaxle 37 extends above and below the roll 36 and is slidably received inslots 38 in the rear ends of the arms 30 and 31. The ends of the axle 37extending into the slots 38 are slidably received over set screws 39threadedly positioned in the slots 38. A spring 40 encircles each setscrew 39 between the head thereof and the axle 37 so that the roll 36 isconstantly urged forwardly toward the roll 34.

The rolls 34 and 36 receive the guide bar 20 therebetween to control theposition of the saddle 25 as the carriage 18 moves along the bed 16.Since the arms 30 and 31 are pivoted about the common vertical axis 32,the entire unit comprised of the rolls 34 and 36 and the arms 30 and 31can pivot to insure proper contact of the rolls 34 and 36 as the off-setportion 22 of the bar 20 is engaged.

Since the guide rolls 34 and 36 are always maintained parallel to eachother and parallel to the vertical axis 32, the semi-circular portion 22of the guide bar 20 may be selectively pivoted in the brackets 21 todefine different arcs through which the guide rolls 34 and 36 willtravel as the carriage 18 is moved along the length ofthe bed 16. Thus,the amount of extension and retraction of the slide 25 along the slideplate 26 as the carriage 18 is moved, is controlled by the semicircularbar 20.

As shown in FIGS. 1, 2 and 3, an indicator mechanism M and the cutterassembly A are mounted on the carriage 18 so that the mechanism M andassembly A are both moved toward and away from the tire and wheel.assembly TW as the carriage 18 is moved back and forth along the line ofmotion C and the saddle 25 is moved toward and away from the tire andwheel assembly TW along the line of motion B in response to thesemicircular portion 22 of the guide bar 20.

The cutter assembly A is of conventional design having a motor 46 and acutter 48. The cutter assembly A is mounted on the carriage 18.

The indicator mechanism M is mounted on top of the carriage 18 by amounting plate 52 attached to the block through a plurality of bolts 54.The mounting plate 52 pivotally mounts the indicator mechanism M thereonas will be explained hereinafter.

As best seen in FIGS. 4-9, the first embodiment of the indicatormechanism M includes generally a support frame 55 which mounts a firstindicator 56, a second indicator 58, and a third indicator 59 thereon.An adjustment mechanism is carried by the support frame 55 and isoperatively connected to the first indicator 56 and third indicator 59to selectively adjust the spacing between the indicators 56, 58 and 59.It will be noted that the first indicator 56 is utilized to measure theradial deviations along one edge of the tire tread 13, that the secondindicator 58 is utilized to measure the radial deviations along thecenter of the tire tread 13, and that the third indicator 59 is utilizedto measure the radial deviations along the opposite edge of the tiretread 13. The indicator mechanism M is utilized by aligning theindicator 58 with the center of the tire tread l3 and selectivelyadjusting the adjusting the adjusting mechanism 60 until the indicator56 is in alignment with one edge of the tread l3 and the indicator 59 isin alignment with the opposite edge of the tire tread 13. The guide bar20 is then moved until the line AL is centered between the rolls 34 and36 and locked in place by handle 24. This centers the bar 20 withrespect to the tread 13. T

The support frame 55 includes a horizontally oriented L-shaped beam 61longitudinally extending across the indicator mechanism M and providedwith upstanding end plates 62 at opposite ends thereof. The end plate 62are provided at their rearmost corners with mounting apertures 64through which a horizontal pivot shaft 65 extends. The pivot shaft 65 issupported at its central portion by a bearing block 66, as seen in FIGS.8 and 9, fixedly carried by the L-shaped beam 61. The pivot shaft 65 isrotatably received through the forward portion of the mounting plate 52so that the frame 55 carrying the indicators 56, 58, and 59 can bepivoted thereabout.

As best seen in FIGS. 6 and 7, the indicator 56 comprises generally acrescent shaped support bracket having a rearwardly extending protrusion71 integral therewith. The protrusion 71 defines an aperture 72 throughits rearmost corner for pivotally mounting the bracket 70 on the pivotshaft 65 and is provided with a threaded sleeve 77 extending through thebracket 70 at the junction of the crescent B and the projection 71 andaffixed thereto. The sleeve 77 is connected with the adjusting mechanism60 to move the support bracket 70 along the shaft 65 while maintainingthe support bracket 70 substantially perpendicular thereto.

The forwardmost edge of the crescent shaped member 70 pivotally mounts alink 74 on the inside thereof and pivotally mounts a triangular cam 75on the outside thereof. A wheel 76 is pivotally mounted between theforwardmost extending corner of the triangular cam 75 and the extendingend of the link 74 for free rotational movement therebetween. Thereforeit will be seen that the wheel 76, link 74 and cam 75 pivot with respectto the bracket 70 and the wheel 76 rotates with respect to the link 74and cam 75.

The rearmost extending camming comer 78 of the cam 75 extends rearwardlytoward the other end of the crescent B of the member 70. A carriageplate 79 having the shape of a sector of a circle is pivotally mountedat the other end of the crescent B of the member 70 whereby the frontcamming edge 80 thereof lies against the rearmost camming comer 78 ofthe triangular shaped cam 75. A spring 81 connected between theforwardmost extending corner of the triangular shaped cam 75 and thecarriage plate 79 forces the cam 75 and the carriage plate 79 towardeach other. A semicircular indicator plate 82 is attached along theoutermost edge of the carriage plate 79 and extends substantiallyparallel to the axis about which the carriage plate 79 pivots.Therefore, it can be seen that as the wheel 76 is pivoted rearwardly,the camming comer 78 of the cam 75 forces the carriage plate 79 to pivotrearwardly or clockwise as seen in FIG. 6. This also moves the indicatorplate 82 rearwardly. When the wheel 76 is not forced rearwardly, thespring 81 forces the carriage plate 79 forwardly or counterclockwise asseen in FIG. 6 and forces the wheel 76 forwardly again to its initialposition.

The indicator 59 is substantially identical in construction to theindicator 56 and the corresponding parts thereof will be indicated byprimes of the reference numerals applied to the components of theindicator 56.

As best seen in FIGS. 8 and 9, the indicator 58 comprises generally apair of crescent shaped support brackets 90 integral with the bearingblock 66 and extending upwardly therefrom between and in lateralalignment with the crescent shaped support brackets 70 and 70. Thesupport brackets 90 are spaced apart and parallel to each other. Thebrackets 90 each carry a backing plate 91 along the outer peripherythereof which are arcuate in shape. Pivoted to the forwardly extendingend of the crescents C of the brackets 90 is an indicator wheel 92rotatably mounted between links 94 pivoted on the outside of theforwardly extending ends of the crescents C. The wheel 92 is constantlyurged forwardly by a spring- 96 until the movement thereof is checked bythe links 94 engaging the arcuate plates 91.

An indicator arm 98 is pivoted between the support brackets 90 at therearmost end of the crescents C of the brackets 90 and is connected 'tothe wheel 92 through a linkage 99 so that as the Wheel 92 is movedrearwardly, the indicator arm 98 will also be pivoted rearwardly orclockwise in FIG. 8. The indicator arm 98 carries along the arcuateouter end thereof an arcuate indicator plate 100 which overlies theedges of the indicator plates 82 and 82' and the backing plates 91.

The adjusting mechanism 60 includes a horizontal threaded shaft 101 asbest seen in FIG. rotatably mounted in the end plates 62 and the bearingblock 66 and provided with a right hand threaded portion 102 on theright end thereof as seen in FIG. 5 and a left hand threaded portion 104on the left end thereof as seen in FIG. 5. As the shaft 101 is rotated,the threaded sleeves 77 and 77 extending through the brackets 70 and 70'will be driven toward each other or away from each other simultaneously.In this manner, the wheel 92 always remains centered between the wheels76 and '76. A conventional handle 105 is provided on one end of thethreaded shaft 101 extending through one of the end plates for rotatingthe same and adjusting the spacing between the indicators 56, 58 and 59.This allows the mechanism M to be used with tire and wheel assemblies TWof different tread widths.

As best seen in FIG. 12, the indicator plate 82 is provided with aradial deviation indicator line 110 and the indicator plate 82' isprovided with a corresponding radial deviation indicator line 111. Theindicator plate 100 is provided with a radial deviation indicator line 112. The indicator plate 82 is also provided with a plurality of treadcurvature lines 113 which in combination with the radial deviationindicator line 112 on the indicator plate 100, indicate the pivotalsetting of the guide bar 20 so that original tire tread shape can bemaintained during the tire stabilizing operation.

To indicate the difference in radial deviation between that edge of thetread 13 associated with the indicator plate 82 that edge of the tread13 associated with the indicator plate 82', an extension 114, as bestseen in FIG. 12, is provided. The extension 114 is connected tothe-indicator plate 82 for movement therewith and extends across theinterior mechanism M and over the indicator plate 82. A pointer 115 isprovided which remains in alignment with the radial deivation indicatorline 111 on the indicator plate 82' and overlies the radial deviationindicator line on the indicator plate 82 to indicate the absolutedeviation between the opposite edges of the tread 13 of the wheel andtire assembly TW.

A dial cover plate 120, as best seen in FIG. 11, is provided for theindicator mechanism M and includes an arcuate dial member 121 havingdepending end plates 122, as seen in FIG. 5, at each end thereofconnected to the frame 55. The dial member 121 has the same curvature asthe indicator plates 82, 82' and 100 overliesthe same. A plurality ofwindows W are provided in the dial member 121 under which the radialdeviation indicator lines 110, 111, and 112 and the pointer move toindicate tread curvature, radial runout, and lateral runout.

One of the windows W referenced by the numeral 125 overlies a portion ofthe indicator plate 82 and also overlies the pointer 115 connected tothe indicator plate 82'. the window 125, then, indicates the absolutedifference between the radial runout of the edges of the tread 13 of thetire and wheel assembly TW. This measures the effect of the lateralrunout of the tread 13. The window 125 is provided with appropriateindicia I to indicate the amount of lateral runout in the tire and wheelassembly TW.

A window 126 is spaced from the window 125 and overlies the indicatorplate 82 with its radial deviation indicator line 1 10 so as to indicatethe radial deviations or radial runout of that edge of the tread 13associated with the indicator 56. The window 126 has appropriate indiciaI thereon to indicate the amount of radial runout along that edge of thetread 13 associated with the indicator 56 as the tire and wheel assemblyTW rotates by the indicator 56.

A window 128 overlies the junction of the indicator plate 100 and theindicator plate 82 to indicate the tread curvature ofthe tire and wheelassembly TW for setting theguide bar 20 and control the cutting of thetread 13. The window 128 is clear. The radial deviation indicator 112 onthe indicator plate 100 moves with respect to the indicator plate 82 andoverlies one of a plurality of the thread curvature lines 1 13 on theindicator plate 82 to indicate the angular setting of the guide bar 20.

A window 129 overlies the indicator plate 100 and its deviationindicator line 1 12 to indicate the radial deviations along the centerof the tread 13. The window 129 has appropriate indicia I thereon justas the window 126 to indicate the amount of radial deviation or radialrunout along the center of the tread 13.

A window 130 overlies the indicator plate 82' and is associated with theradial deviation indictor line 111 to indicate the radial deviationsalong that edge of the tread 13 associated with the indicator S9.Appropriate indicia I are provided on the window 130 to indicate theamount of radial runout associated with that edge of the tread 13associated with the indicator 59.

The bottom of the L-shaped member 61 rests on the top of the mountingblock 52 to properly position the indicator mechanism M for measuringthe tire and wheel assembly TW. To insure that the indicator mechanism Mwill stay in this position, a U-shaped wire member W with its legs Lslidably extending through appropriate holes H through the mountingbracket 52 is provided. The legs L slide through the mounting bracket 52and just over the L-shaped member 61 of the frame 55 to lock it inposition. When the legs L are retracted within the mounting bracket 52,theindicator mechanism M may be pivoted out from over the cutterassembly A so that the tire and wheel assembly TW may have its tread 13redefined by the cutter 48 to stabilize the same while it rotates. Whenthe indicator mechanism is in its down position for measuring the tireand wheel assembly TW. it serves as a protective cover for the cutter48.

A positioning dial 140 as seen in FIG. is mounted on one of the mountingbrackets 21 adjacent the guide bar 20. The dial 140 has indicia 141thereon corresponding to the numbering of the lines 113 on the indicator56. A groove 142 is formed in the guide bar and extends past the indicia141 on the dial 140. The dial 140 and groove 142 are so arranged so thatthe tread curvature indicated by the indicators 56 and 58 will beretained when the corresponding setting is made between the dial 140 andthe pointer 142. In other words, the nearer the offset portion 22 of theguide bar 20 is to the vertical the flatter the tread 13 will be acrossits width. In this manner, the original tread curvature of the tread 13will be retained during the cutting operation.

SECOND EMBODIMENT Referring to FIGS. 13 and 14, it will be seen that asecond embodiment of the indicator mechanism M serves the same purposeas the first embodiment of the indicator M but measures tread curvature,radial runout, and the effect of lateral runout electronically. Theindicator mechanism M comprises generally a housing which is carried onthe mounting block 45. The housing carries a first indicator 256, asecond indicator 258 and the third indicator 259 therein. An'adjustingmecha nism 260 similar to the adjusting mechanism 60 of the firstembodiment of the indicator mechanism M is provided for selectivelyspacing the indicators 256, 258 and 259 with respect to each other inthe same manner as the indicators 56, 58 and 59 are-spaced with respectto each other. This allows the indicator mechanism M to be used withtires having different tread widths.

The indicators 256, 258 and 259 are sensing units commercially availableon the market today to acurately determine the distance between anobject and the indicator head. One type sensing head that will achievethis function is available under the name of Electro-Optical Systems andmanufactured by Physitech, Inc. of Willow Grove, Pennsylvaina.

The indicator 256 is connected to a radial readout control unit 500, theindicator 258 is connected to a radial readout control unit 501, and theindicator 259 is connected to a radial readout control unit 502. Thecontrol units 500, 501 and 502 are connected in parallel to a voltagesource 504 which supplies current thereto. The control unit 500 isconnected to a radial readout meter 505, the control unit 501 isconnected to a radial readout meter 506 and the control unit 502 isconnected to a radial readout meter 508. It will be understood that thecontrol units 500, 501 and 502 supply an output to the meters 505, 506and 508 in response to the indicators to indicate the radial runout ofthe tread 13 adjacent each of the indicators 256, 258 and 259.

The indicators 256 and 259 are also connected to a conventionalcomparator 509 which is in turn connected to a lateral readout meter510. The comparator 509 is operatively connected to the voltage source504 in parallel with the control units 500, 501 and 502. It will beunderstood that the comparator 509 compares the output of the indicators256 and 259 to indicate the maximum absolute difference in radial runoutbetween the indicators 256 and 259 to give a lateral runout reading.

The indicators 256 and 258 are connected to another conventionalcomparator 511 which is in turn connected to a tire curvature meter 512.The comparator 511 is also connected to the voltage source 504 inparallel with the comparator 509 and the control units 500, 501 and 502.It will be understood that the comparator 511 compares the radial runoutoutputs from .the indicators 256 and 258 to indicate the curvature ofthe tire across its tread.

TI-IIRD EMBODIMENT Referring to FIGS. 17 19, the third embodiment of theindicator mechanism M is indicated generally by the reference numeral M.The indicator mechanism M is used in the same manner as the indicatormechanism M. The indicator mechanism M is pivotally mounted by mountingplate 52 and carried by the mounting block 45. A base plate 300 isincluded in the indicating mechanism M which is pivotally mountedbetween the upstanding ends of the mounting plate 52' by a pivot shaft301 extending through the mounting plate 52' and the base member 300.The base member 300 defines a slide plate 302 thereon which extendsalong the line of motion B and which mounts thereon a saddle 304. Thesaddle 304 is urged forwardly by a spring 305 extending between the rearof the saddle 304 and the base member 300. An indicator wheel assembly306 is pivotally mounted on the top of the saddle 304.

The indicator-wheel assembly 306 includes a centrally located bearingplate 308 which mounts a pair of spaced parallel guide rods 309 thereon.The guide rods 309 extend outwardly from the right and left side of thebearing plate 308 as seen in FIG. 18 parallel to the line of motion C.An indicator arm 310 is carried on the right end of the guide rods 309as seen in FIG. 18 and corresponding indicator arm 311 is carried on theleft end of the guide rods 309 as seen in FIG. 18. The indicator arm 310and 311 extend parallel to each other and parallel to line of motion Btoward the wheel and tire assembly TW. Appropriate guide members notshown are provided on the indicator arms 310 and 311 to provide for theslidable movement thereof toward and away from the bearing plate 308while remaining parallel to each other and parallel to the line ofmotion Ii.

An adjustment screw 314 is also rotntuhly mounted on top of the bearingplate 308 and extends outwardly therefrom to the right and to the leftas seen in FIG. 18 to position the indicator arms 310 and 311. Theadjustment screw 314 is provided with left hand threads 315 on the rightside thereof as seen in FIG. 18 and with right hand threads 316 on theleft side thereof as seen in FIG. 18. An appropriate handle 318 isprovided on the extending end of the adjustment screw 314 for rotatingthe same. Appropriate threaded bosses 319 are provided on the indicatorarms 310 and 311 which threadedly engage the threads 315 and 316 of theadjusting screw 314. As the handle 318 is rotated, the adjustment screw314 simultaneously moves the indicator arms 310 and 311 toward eachother or away from each other. An indicator wheel 320 is rotatablymounted in the forwardly extending end of the indicator arm 310 and anindicator wheel 321 is rotatably mounted in the forwardly extending endof the arm 311. The indicator wheels 320 and 321 rotate about a commonaxis and the adjusting mechanism 14 may be manipulated to move theindicator wheels 320 and 321 along the line of motion B until theycontact the tread 13 of the tire and wheel assembly TW.

The indicator arms 310 and 311 and the bearing plate 308 may pivot aboutthe pivot point 322 as best seen in FIG. 19. As the indicator wheels 320and 321 engage the tread 13 of the tire and wheel assembly TW, and thetire and wheel assembly TW is rotated, the indicator wheels 320 and 321will pivot the bearing plate 308 in accordance with the absolutedifference d in radial deviation between the edges of the tread 13 alongan imaginary line running transversely off the tread 13. This gives adirect reading of the effect of the lateral runout. An appropriate dial324 is provided on the saddle 304 and a pointer 325 is provided on theforwardly extending end of the bearing plate 308 so that the amount oflateral runout will be indicated directly as the tire and wheel assemblyTW is rotated.

For determining the radial deviations or radial runout of the tread 13,an indicator strip 326 having indicia I thereon is provided along theupper surface of the base member 300 adjacent the front edge 329 of thesaddle 304. By moving the indicator wheels 320 and 321 along the line ofmotion B until the saddle 304 is zeroed on the indicator strip 326, thespring 305 will maintain the indicator wheels 320 and 321 against thetire tread 13 as the same rotates thereby. The spring 305 forces thesaddle 304 to move back and forth in accordance with the radialdeviations d in the tread 13. The operator then, can directly read theamount of radial runout in the tread 13. This embodiment of theindicator mechanism reduces the components thereof to an absoluteminimum while still giving all of the necessary indicia to determine theeffect of radial and lateral runout of j the tire and wheel assembly TW.

OPERATION and wheel assembly TW for checking the irregularities in thetread l3 and a second speed for rotating the turning wheel assembly TWduring the cutting operation with the cutter assembly A. The first speedis relatively slow whereas the second speed is much faster for thecutting operation.

When the first embodiment of the indicator mechanism M is used, themechanism M is pivoted to its down position so that it overlies thecutter 48 of the cutter assembly A and the wire member W is moved so asto lock the mechanism M in this down position. The locking screw 24 inthe mounting bracket 21 is manipulated so as to release the guide-bar 20for slidable movement of the guide bar 20 along its length as well aspivoting about its centerline. The adjustment wheel and screw assemblies14 and 19 are manipulated until the wheel 92 of the indicator 58 isapproximately centered on the tread 13 of the tire and wheel assembly TWmounted on the spindle S.

The handle of the indicator mechanism M is then manipulated along withthe wheel and screw assembly 19 until the indicator wheels 76 and 76rest on opposite edges of the tread 13. This centers the indicatormechanism M with respect to the tire and wheel assembly TW. Theadjustment wheel and screw assembly is then manipulated to move theindicator mechanism M toward the tread 13 until the indicator line ofthe indicator 56 is zeroed under the window 125 in the cover 120. Thisgives a fixed point from which the readings on the indicator mechanism Mare made.

The tire tread 13 is slowly rotated in contact with the indicatormechanism M. As the tire wheel assembly TW is rotated, the indicatorwheels 76, 76' and 92 are moved in response to the varying radiusbetween the center of rotation of the tire and wheel assembly TW and thetread 13. This causes the earns 75 and 75' to engage and move thecarriage plates 79 and 79' in response to the pivotal movement of thewheels 76 and 76' and the links 74. As the carriage plates 79 and 79 aremoved, the indicator lines 110 and 11 1 are moved under their associatedwindows W. It will also be noted that the pointer will be moved alongover the indicator plate 82 as the indicator plate 82 is moved.

In like manner, it will be seen that the indicator arm 98 of theindicator 58 is moved in response to the pivotal movement of the wheel92 and links 94 through the linkage '99. This moves the indicator plate100 with its associated indicator line 112 under the cover 120.

The operator watches the movement of the indicator lines 110, 111, and112 as well as the movement of pointer 115, as the thread 13 is slowlyrotating in contact with the indicators 56, 58 and 59. The operatornotes the maximum difference between the indications represented by theindicator line 112 and the pointer 1 15 to determine the amount of treadre-definition that is necessary to remove the radial runout and theeffect of lateral runout. The operator also notes the amount of radialrunout associated with each indicator 56, 58 and 59 to determine theamount of tread of redefinition that is necessary to remove the effectof radial runout. The operator will also note which one of the curvaturelines 113 is indicated by the indicator line 112 under the window 128.This indicates to the operator the rotational position at which he mustset the guide bar 20 to re-define the tread so that the same treadcurvature across the width of the tread is retained.

After the operator has made these determinations, he moves the guide bar20 longitudinally along its center line and parallel to the line ofmotion C until the line AL described on guide bar 20 is centered betweenthe rolls 34 and 36. This insures that the cutter assembly A willredesign the tread 13 symmetrically across its width during the cuttingoperation. The operator then pivots the guide bar 20 about its centerline until the pointer 122 adjacent the positioning dial 140 lies overthe indicia 141 indicated by the indicator line 112 under the window128. This insures that the cutter assembly A will be moved in responseto the off-set portion 22 of the guide bar 20 during the cuttingoperation to redefine the tread 13 with the same curvature across itswidth as the original tread had.

The operator then moves the wire member W so as to release the indicatormechanism M for pivoting, pivots the indicator mechanism M up out of theway and manipulates the adjusting wheel and screw assembly 14 to movethe cutter assembly A into contact with the tread 13. The motor 46 ofthe cutter assembly A is energized to rotate the cutter 48, and theadjusting wheel and screw assembly 19 is manipulated to move the cutterassembly A across the tread 13 to re-define the same. It is possible forthe operator to further manipulate the adjusting wheel and screwassembly 14 to move the cutter assembly A further toward the center ofrotation of the tread 13 to remove a sufficient amount of rubber fromthe tread 13 to re-define the same to form a substantially perfectcylinder about the axis of rotation of the tire and wheel assembly TW.

After the tread 13 has been re-defined, the operator retracts the cutterassembly A away from the tread 13 by manipulating the wheel and screwassembly 14, removes the tire and wheel assembly TW from the spindle Sand re-installs the same on the vehicle. The wheel and tire assembly TWis now stabilized for rotation about its effective rotational axis.

' In using the second embodiment of the indicator mechanism designatedas M, it will be seen that the operator mounts the tire and wheelassembly Tw in the same manner, pivots the indicator mechanism M to itsdown position as was done with the first embodiment of the indicatormechanism M and moves the indicator mechanism M into close proximitywith the tread 13.

The basic difference between the indicator mechanism M and the indicatormechanism M is that it is not necessary for the indicator mechanism M toactually contact the tread 13 to measure the effect of radial andlateral runout as well as tread curvature across its width. Theadjustment mechanism 260 of the indicator mechanism M is manipulated toproperly adjust the spacing between the indicators 256, 258 and 259similarly to the adjustment of the indicators 56, 58 and 59 by thehandle 105 of the adjustment mechanism 60. The operator zeros theindicator mechanism M by manipulating the adjustment wheel and screwassembly 14 until the radial readout meter 505 is zeroed. This gives areference point from which to work with the indicator mechanism M.

The operator then watches the meters 505, 506, 508, I

510 and 512 to determine the curvature of the tread across its width toset the guide bar 20, the amount of tread re-definition necessary tocorrect the effects of lateral runout, and the amount of treadre-definition necessary to correct the effects of radial runout. Thetire and wheel asselbly TW is then rotated in the aforementioned manner,the guide bar 20 set in the same way, and the tread l3 redefined in thesame way as with the first embodiment of the indicator mechanism M.

The third embodiment of the indicator mechanism M" is used insubstantially the same manner as the first embodiment thereof. In thisembodiment of the indicator mechanism M", there is no middle indicatorso that the handle 318 is manipulated to properly space the indicatorwheels 320 and 321 along each edge of the tread and then the indicatorM" is moved up against the tread 13 using the wheel and screw assemblies14 and 19. The indicator mechanism M" is so moved until the front edge328 of the plate 304 is zeroed on the indicia I of the indicator strip328.

The operator then notes the amount of deviation at any opposite pointsalong the tread 13 as the tire and wheel assembly TW is rotated toindicate the amount of rubber that must be removed from the tire andwheel assembly TW to re-define the tread 13. Reference to the indicatorstrip 328 will also tell the operator the amount of radial deviationalong the tread 13.

It will be noted that the third embodiment of the indicator mechanism M"does not indicate the setting of the guide bar 20 to re-define the treadcurvature 13 across its width. This is done using a set of templates.

While specific embodiments of the invention have been disclosed herein,it is to be understood that modifications, substitutions and equivalentsmay be used without departing from the scope of the invention as setforth by the appended claims.

We claim:

1. A method of stabilizing a vehicular wheel and tire assembly rotatableabout an axis and having a circumferential tread which rolls along asurface comprising the steps of:

a. rotating said tire and wheel assembly about said axis whilesimultaneously determining the radial deviations at least at two axialspaced points along a common line extending across said tread;

b. correlating the determinations thus taken to indicate the maximumabsolute difference between any two radial deviations thus taken alongsaid line; and,

c. subsequently cutting away selected portions of said tread so thatsaid maximum absolute difference is not greater than a predeterminedamount.

2. The method of claim 1 wherein said predetermined amount issubstantially zero.

3. The method of claim 2 further including the step of determining thecurvature of said tread and wherein thestep of cutting away selectedportions of said tread includes redefining a tread having the samecurvature as said original tread.

4. The method ofclaim 2 wherein said determination of said radialdeviations is performed mechanically.

5. The method of claim 2 wherein said determinations of said radialdeviations is performed electronically.

6. Apparatus for stabilizing a vehicular wheel and tire assemblyrotatable about an axis and having a circumferential tread which rollsalong a surface including:

a. support means for mounting and rotating said wheel and tire assemblyabout said axis;-

b. indicator means adjustably carried by said support means adjacent thetread, said indicator means constructed and arranged to simultaneouslymeasure the radial deviations in the tread at least at two axial spacedpoints along a common line extending across said tread as the tread isrotated; and,

c. cutter means adjustably carried by said support means for cuttingaway selected portions of the tread.

7. The apparatus of claim 6 further including guide means forcontrolling the movement of said cutting means.

8. The apparatus of claim 6 wherein said indicator means includes:

a. a first indicator engaging said tread;

b. a second indicator spaced from said first indicator, aligned withsaid first indicator, and engaging said tread as said tread is rotated;and,

c. adjusting means for selectively varying the spacing between saidfirst and second indicators.

9. The apparatus of claim 8 further including means connecting saidfirst and second indicators for correlating the measurements taken byeach to indicate the maximum absolute difference between themeasurements.

10. The apparatus of claim 8 further including a third indicatorengaging said tread as said tread is rotated and aligned with said firstand second indicators, and wherein, said adjusting means maintains saidthird indicator centered between said first and second indicators.

11. The apparatus of claim 8 wherein said indicator means includes:

a base plate pivotally mounted on said support means;

a saddle slideably mounted on said base plate, means for urging saidsaddle toward said tread along a first line of motion;

a bearing plate pivotally mounted on said saddle about an axisperpendicular to said line of motion;

said first indicator being carried by said bearing plate and including:

a first arm adjustably carried by said bearing plate and extendingtoward said tread, said arm being moveable with said bearing plate, and

a wheel rotatably mounted on said first arm at that end extending towardsaid tread;

said second indicator being carried by said bearing plate and including:I

a second arm adjustably carried by said bearing plate parallel to andaligned with said first arm, said second arm being moveable with saidbearing plate, and

a second wheel rotatably mounted on said second arm at the end extendingtoward said tread.

12. The apparatus of claim 8 wherein said indicator means includes:

a support frame pivotally mounted on said support means,

said first indicator being carried by said support frame and including:

a first support bracket mounted on said support frame and extendingtoward said tread,

link means pivotally mounted at one end thereof on the end of said firstbracket extending toward said tread,

a wheel rotatably mounted on the other end of said link means,

camming means carried by said link means and moveable therewith,

a carriage plate pivotally mounted on said first bracket and engaged bysaid camming means for pivoting said carriage plate as said link meansis moved, and

resilient means for urging said camming means into engagement with saidcarriage plate and for urging said wheel toward said tread;

said second indicator being carried by said support frame and including:

a second support bracket mounted on said support frame and extendingtoward said tread,

link means pivotally mounted at one end thereof on the end of saidsecond bracket extending toward said tread,

a second wheel rotatably mounted on the other end of said link means, 7

camming means carried by said link means and moveable therewith,

a carriage plate pivotally mounted on said second bracket and engaged bysaid camming means for pivoting said carriage plate as said link meansis moved, and

resilient means for urging said camming means into engagement with saidcarriage plate and for urging said wheel toward said tread.

1. A method of stabilizing a vehicular wheel and tire assembly rotatableabout an axis and having a circumferential tread which rolls along asurface comprising the steps of: a. rotating said tire and wheelassembly about said axis while simultaneously determining the radialdeviations at least at two axial spaced points along a common lineextending across said tread; b. correlating the determinations thustaken to indicate the maximum absolute difference between any two radialdeviations thus taken along said line; and, c. subsequently cutting awayselected portions of said tread so that said maximum absolute differenceis not greater than a predetermined amount.
 2. The method of claim 1wherein said predetermined amount is substantially zero.
 3. The methodof claim 2 further including the step of determining the curvature ofsaid tread and wherein the step of cutting away selected portions ofsaid tread includes redefining a tread having the same curvature as saidoriginal tread.
 4. The method of claim 2 wherein said determination ofsaid radial deviations is performed mechanically.
 5. The method of claim2 wherein said determinations of said radial deviations is performedelectronically.
 6. Apparatus for stabilizing a vehicular wheel and tireassembly rotatable about an axis and having a circumferential treadwhich rolls along a surface including: a. support means for mounting androtating said wheel and tire assembly about said axis; b. indicatormeans adjustably carried by said support means adjacent the tread, saidindicator means constructed and arranged to simultaneously measure theradial deviations in the tread at least at two axial spaced points alonga common line extending across said tread as the tread is rotated; and,c. cutter means adjustably carried by said support means for cuttingaway selected portions of the tread.
 7. The apparatus of claim 6 furtherincluding guide means for controlling the movement of said cuttingmeans.
 8. The apparatus of claim 6 wherein said indicator meansincludes: a. a first indicator engaging said tread; b. a secondindicator spaced from said first indicator, aligned with said firstindicator, and engaging said tread as said tread is rotated; and, c.adjusting means for selectively varying the spacing between said firstand second indicators.
 9. The apparatus of claim 8 further includingmeans connecting said first and second indicators for correlating themeasurements taken by each to indicate the maximum absolute differencebetween the measurements.
 10. The apparatus of claim 8 further includinga third indicator engaging said tread as said tread is rotated andaligned with said first and second indicators, and wherein, saidadjusting means maintains said third indicator centered between saidfirst and second indicators.
 11. The apparatus of claim 8 wherein saidindicator means includes: a base plate pivotally mounted on said supportmeans; a saddle slideably mounted on said base plate, means for urgingsaid saddle toward said tread along a first line of motion; a bearingplate pivotally mounted on said saddle about an axis perpendicular tosaid line of motion; said first indicator being carried by said bearingplate and including: a first arm adjustably carried by said bearingplate and extending toward said tread, said arm being moveable with saidbearing plAte, and a wheel rotatably mounted on said first arm at thatend extending toward said tread; said second indicator being carried bysaid bearing plate and including: a second arm adjustably carried bysaid bearing plate parallel to and aligned with said first arm, saidsecond arm being moveable with said bearing plate, and a second wheelrotatably mounted on said second arm at the end extending toward saidtread.
 12. The apparatus of claim 8 wherein said indicator meansincludes: a support frame pivotally mounted on said support means, saidfirst indicator being carried by said support frame and including: afirst support bracket mounted on said support frame and extending towardsaid tread, link means pivotally mounted at one end thereof on the endof said first bracket extending toward said tread, a wheel rotatablymounted on the other end of said link means, camming means carried bysaid link means and moveable therewith, a carriage plate pivotallymounted on said first bracket and engaged by said camming means forpivoting said carriage plate as said link means is moved, and resilientmeans for urging said camming means into engagement with said carriageplate and for urging said wheel toward said tread; said second indicatorbeing carried by said support frame and including: a second supportbracket mounted on said support frame and extending toward said tread,link means pivotally mounted at one end thereof on the end of saidsecond bracket extending toward said tread, a second wheel rotatablymounted on the other end of said link means, camming means carried bysaid link means and moveable therewith, a carriage plate pivotallymounted on said second bracket and engaged by said camming means forpivoting said carriage plate as said link means is moved, and resilientmeans for urging said camming means into engagement with said carriageplate and for urging said wheel toward said tread.